Conventional MPEG-2 decoders typically do not have any capability for special handling of progressive refresh bitstreams, which do not contain intra-pictures (I-pictures), and in which a portion of each prediction-picture (P-picture) is independently decodable. In progressive refresh bitstreams, the decodable portion of each P-picture in a set of P-pictures typically moves from top to bottom, starting at the top of the first P-picture in the set and ending at the bottom of the last P-picture in the set. Hence, no P-picture is completely refreshed (or decoded) until a set of P-pictures has been decoded so that each portion of an entire picture area is refreshed in at least one of the P-pictures. Thus, display of artifacts is often unavoidable after channel acquisition (e.g., due to switching channel) since the first few anchor pictures are typically not completely refreshed P-pictures.
Therefore, it is desirable to provide an apparatus and method for preventing artifacts from being displayed after channel acquisition.